There are numerous situations and applications where it is desirable and/or necessary to secure or support one object to or on another object whilst allowing for freedom of translational or rotational movement of these objects relative to one another.
In the field of material handling, for example, roller conveyors are used to transport sheet metal and other ferromagnetic work pieces from one location to another. Gravity forces are relied upon to ensure the work pieces remain on the conveyor rollers (some of which may be driven and others being idle rollers) as these are transported, and thus such conveyor systems will mostly have roller transport paths extending substantially in a common horizontal plane, unless additional, dedicated hold-down structures are employed in restraining the work pieces from lifting-off from where rollers are deployed along inclined travel path sections.
In overhead conveying applications in enclosed surroundings, eg large ware houses, it is known to install overhead rails to which are secured wheeled carriages from which in turn may be suspended crane head structures, grippers and similar attachment devices. Gravity force is relied upon to hold the grooved carriage wheels in engagement with and on top of the overhead guide rails, and side brackets provide additional security against lateral dislodgement from the rails.
In the field of high-rise building construction, it is known to provide vertically extending rails which provide guidance for working platforms which are suspended for vertical movement from the top of the building in order to carry out maintenance work, such as window cleaning, etc. The platforms incorporate gripper mechanisms which form-fittingly engage over the rails to restrain horizontal movement (eg swaying) whilst held vertically movable along the rail.
In the field of robotics, in particular such using remote controlled vehicles, it is known to incorporate into autonomous, wheeled platform or self-tracked vehicles, a multitude of different type of tools and implements by way of which specific tasks may be carried out remotely by an operator. For example, gripper-arms can be deployed from such vehicles to recover samples in difficult to access or hostile environments. Whilst friction enhancing wheel and track coatings may be used to increase adherence of the vehicle to the surface in order to allow the vehicle to climb or descend along steep inclines, there are limits to the steepness of the travel path which such vehicle may safely master without tipping over or sliding in uncontrolled manner.
The present invention was conceived having regard to applications such as those listed above, and in particular to one or more application environments where (a) ferromagnetic materials require conveying or transporting, (b) the incorporation of or presence of ferromagnetic structures would allow the use of magnets as a source of force to secure objects to one another in displaceable manner, (c) gravitational forces are absent to provide for force-locking engagement of a movable object onto a dedicated ferromagnetic material substrate or support surface, or (d) indeed the presence of gravitational forces would necessitate the erection of or provision of specialised support, guide or other retention structures or measures to enable a vehicle, either self-propelled or otherwise, to move along steeply inclined, vertical, and even inclined or horizontal overhanging (eg ceiling) surfaces having ferromagnetic properties. However, the below disclosed invention and its underlying principles may find broader applications, also replacing existing solutions currently not employing magnetic force to achieve object coupling.
In using particular permanent magnets to secure objects to one another, it is known that the magnetic attraction force is a function of the type and amount of active magnetic material employed, the geometry of the magnet's working face, air or other magnetic leakage paths in the magnetic flux circuit encompassing the active magnetic material and the body being subjected to the magnetic attraction force, the ferromagnetic material properties of the attracted body (ie its relative permeability and magnetic saturation limits), and the orientation of the Normal force vector between attracted objects relative to the gravity force vector. The displacement force required will then be a function of the effective attraction force and the coefficient of friction defined between the surfaces of objects.
In other terms, the physical and geometrical factors, as well as the functional energetic elements of the closed (or loaded) magnetic circuit created between a first object (eg an object carrying a permanent magnet) and a second object (eg ferromagnetic sheet) will determine ultimately how strongly the objects are attracted to one another, and whether these objects can be displaced relative to one another whilst remaining attached to one another.
The stronger planar surfaces of objects are ‘forced’ together by a magnetic attraction force, the more difficult it is to displace them relative to one another whilst remaining attached to one another, by exerting a force perpendicular to the attracting force vector, for any given coefficient of friction which applies for the pairing of materials of the two objects. It is also recognised that magnetically attractive surfaces can have very large friction coefficients, and this knowledge has found expression in a wide range of technical solutions, such as magnetic clamps, magnetic lifters, magnetic chucks, etc, where ferromagnetic objects are to be firmly secured against displacement (assuming normal operational condition) at a supporting structure that incorporates magnetic active materials.
In seeking to enable magnetically coupled objects to move more easily relative to one another, so called magnetic wheels have been devised for selected industrial applications, eg self-propelled welding and inspection robots.
In its simplest incarnation, a magnetic wheel may be comprised of a solid disc of permanent magnetic material, eg a disc-shaped Neodymium-Iron-Boron magnet, magnetised such that opposite axial end faces of the magnet have different polarity (here termed axially magnetised). One such disc each can be secured on opposite terminal ends of a non-magnetisable axle member, which in turn can be mounted to a vehicle chassis or frame, whereby the discs may engage with their peripheral surface on a magnetically attractive substrate surface and roll on such surface in a magnetically attached state, compare for example U.S. Pat. No. 6,886,651 (Slocum et al.), column 12, lines 44 following. Each disc (or wheel) will generate an at least partially closed loop magnetic field extending into the substrate on which it rests, creating a strong attractive force between the disc and substrate.
Slocum also discloses a somewhat more elaborate yet simple magnetic wheel consisting of a disc-shaped, axially magnetised magnetic core element sandwiched between two magnetically attractive disc members (made of soft steel, permalloy or laminated structures comprising such magnetisable but otherwise magnetically passive materials) having a diameter that is somewhat larger than the magnet core so that only the disc members can come with their peripheral surfaces into contact with the magnetically attractive surface on which the wheel is to magnetically engage. The disc members thus represent pole extension pieces which concentrate the magnetic flux originating in the magnetic core element and provide a low reluctance path for such flux, thus improving the attractive force between each wheel unit and magnetically attractive support surface as compared to the wheel embodiment without pole extension discs.
Slocum's magnetic wheels are incorporated into self-propelled carriages that form part of a material transportation system wherein such carriages can travel along magnetically attractive surfaces that may include a ceiling, vertical and inclined walls.
U.S. Pat. No. 5,809,099 discloses a laser-guided underwater wall climbing robot for use in inspecting reactor pressure vessels, which robot includes a self-propelled vehicle supperstructure that incorporates four magnetic wheels used to provide the necessary attraction force to allow the vehicle to travel along the ferromagnetic inner surface of the reactor vessel. Each wheel consists of a ring-shaped permanent magnet supported on a non-magnetic axle shaft for rotation therewith, two steel discs of slightly larger diameter than the magnet being magnetically attached and secured to the opposite axial faces of the ring-magnet, ie the discs provide magnetised pole extension pieces as well as the peripheral engagement surface of the wheel unit, similar to the Slocum wheel described above.
U.S. Pat. No. 5,853,655 describes a magnetic wheel guided carriage for automated welding and cutting of ferromagnetic substrates such as pipes, steel plates, wherein the magnetic wheels consist of a plurality (eg three) of axially magnetised ring-shaped magnets sandwiched between interleaving ring-shaped mild steel discs (eg five) of a diameter that is larger than that of the magnets. The stacked discs are mounted and secured against rotation on a stainless steel sleeve which in turn will be received on an axle of the carriage. Again, each wheel unit has a plurality of N- and S-poles whose magnetic field extends into the ferromagnetic substrate thereby creating at each wheel a closed magnetic flux path securing the wheels to the substrate surface.
Other prior art patent documents are also known to deal with aspects and methodologies that seek to address specific shortcomings that ‘basic’ magnetic wheels may exhibit in certain application fields.
So for example, U.S. Pat. No. 3,690,393 (Guy) would seem to aim to address the above mentioned problem that magnetically attractive surfaces can have very large friction coefficients which in certain applications can be detrimental. Guy describes a vehicle having a frame on which is mounted a prime mover (eg electric motor) which is coupled by suitable gearing to a live (or traction) axle to which a pair of wheel assemblies are secured in order to propel the vehicle. In one embodiment, one of the non-driven wheel assemblies consist of a plurality of axially polarised annular magnet discs secured to one another to form a cylindrical roller wheel whose outer (peripheral) surface is coated with a thin layer of a non-polarizable, anti-friction material, such as PTFE (polytetrafluoroethylene) which minimises drag on the wheel assembly as the vehicle frame is propelled.
Guy also describes an electromagnetic wheel assembly, in which a non-magnetic cylindrical shell encloses an electromagnetic coil about an inner core element mounted on the wheel's axle for rotation therewith. Magnetisable pole discs are arranged at the axial ends of the shell member, and electrical energy can be supplied to the magnet coil through wiper contacts secured to one of the pole discs. Upon energization of the electro-magnetic coil, the pole discs will be polarised with opposite polarities. The annular rims of the pole discs are again coated with a non-magnetisable, low-friction material for rolling contact with the magnetisable substrate surface oh which the vehicle is intended to travel.
In contrast, U.S. Pat. No. 2,694,164 (Geppelt) discloses magnetic wheels of a type used in conjunction with welding and cutting torch carriages which are self-propelled over ferromagnetic surfaces. The magnetic wheel units consist of an axle sleeve of non magnetisable material received within an annular-cylindrical permanent magnet which is magnetized in its axial direction, two cylindrically cup shaped wheel members of soft steel material which have their annular flanges extending towards each other and into clamped close engagement with opposite sides of a non-magnetic spacer disc that surrounds the magnet about the middle of its axial length. The axial end faces of the magnet abut against the respectively facing inner faces of the cup wheel members such as to allow magnetic flux transfer from the magnet into the wheels towards their peripheral surface, the spacer disc serving to ensure magnetic decoupling of the two wheels whereby these will assume opposite polarities in accordance with the magnetic field generated by the permanent magnet of the wheel. Geppelt outlines that the decrease in wall thickness of the annular cup flanges towards the spacer disc (as compared to a prior art embodiment with uniform cup flange thickness) increases the attractive force that may be exerted between the magnetic wheel and the substrate to which it attaches.
In practical terms, and in light of the above description of prior art magnetic wheel constructs, a technical challenge still exists in devising methods and arrangements of magnetic flux transfer from a magnet, as a source of magnetic force to attach one object to another, through a wheel structure into a magnetically attractive body, to meet specified operational load carrying capacity or retention requirements.
In a more confined aspect, it would be desirable to provide a vehicle which uses magnetic energy to secure such vehicle onto a ferromagnetic substrate surface and in which the magnetic flux transfer mechanism will allow for greater flexibility with regards to magnetically coupling and decoupling of the vehicle from the substrate surface.
In another more confined aspect, it would be desirable to provide a magnetic support structure by means of which a ferromagnetic object may be transported between locations in a secured manner and wherein at the end of such transporting operation the object may be safely and easily disengaged from the support structure.
In another aspect, it would be desirable to provide a magnetic gripper appliance which may be actuated in order to secure an object thereto whilst allowing for freedom of movement of the object in order to conduct machining or other operations on the object.
The term ‘ferromagnetic’ as used herein is intended to cover not only metals and alloys but also composite materials which when subjected to an external magnetic field will become magnetised and subject to magnetisation forces.
Other aspects of the invention will become apparent below from the following description of preferred embodiments thereof.